CA1139966A - Relative power contribution of an internal combustion engine - Google Patents

Abstract

Relative Power Contribution of an Internal Combustion Engine Abstract The relative power contribution of each cylinder.
in an internal combustion (IC) engine which is connected through a common drive shaft to an engine load and which is running at a selected speed, is provided as the relative magnitudes of each cylinder's contribution to the fluctuations in a sub-cyclic net torque signal pro-vided as the difference torque value between an instan-taneous sub-cyclic engine torque signal and an instan-taneous sub-cyclic load torque signal.

Description

1 -- ' Technical Field This invention relates to the extra-vehicular hot-testing of internal combustion (IC) engines, and more particularly to diagnosing hot-test engine per-5 formance electronically.
Background Art Hot-testing of IC engines outside of a vehicle (extra-vehicular) is known generally, being used mainly in the testing of newly manufactured, production line 10 engines and in the testing of overhauled or repaired ~; engines. me term hot-test refers to testing the engine with ignition to determine basic dynamic engine per-formance. At present the actual tests per-formed during the engine hot-test involve the most basic test criteria 15 and rely almost entirely on the hot-test operator for diagnosing base-line engine performance. Although the tests may involve measurement oE basic engine timing, in general the pass/fail acceptance standards are based on what the operator perceives of the engine running `; 20 characteristics, such as the inability to start or to maintain engine speed, or the sound of the engine while running. m ese tests do provide suitable pass/fail `~ criteria for gross engine malfunctions, however, it is impossible, except to the most experienced operator, to 25 provide even simple diagnosis of the cause of the engine poor performance.
In the first instance, the inability to provide quantitative measurements of engine performance and acceptance, results in`the acceptance of marginal engines .~

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' '' in which the actual failure occurs sometime later as an infant mortality, perhaps after installation in the vehicle. Conversely, the rejection of an engine based on the present qualitative standards may be unwarranted S in many instances, resulting in the unnecessary re-cycling of the engine through some type of repair facility, where with more extensive testing the apparent fault mav be corrected with a minor engine adjustment.
Therefore, it is desirable to establish an accurate quantitative analysis testing procedure which with measurement of selected engine parameters may provide for accurate pass/fail determination.
In the present state of the art of IC engine diagnos-tics electronic analysis has provided superior, quanti-tative test standards for measuring engine performance~These test dia~nostics, however, are intended for testing vehicle mounted engines under test conditions which are of necessity less controlled than those po,en-tially available in the hot-testin~ of engines. One such known test which provides a general indication of overall engine health is the measurement of relative cylinder power contribution for vehicle installed engines as described in U. S. Patent No. 4,064,747 to Rackliffe et al, entitled RELATIVE AND SUB-CYCLIC SPEED MEASURE~NTS
FOR XNTERNAL COMBUSTION E~GINE DIAGNOSTICS and owned by common assignee herewith. This test includes the snap acceleration of the engine loaded only by the rotational inertia of the engine accessory loads with sensed engine speed data being taken along the acceleration profile.
~` ~0 The individual sub-cyclic fluctuations in speed associated ~ith each cylinder are then measured and comp2red as an indication of relative power contribution.
The limitation on the snap acceleration method is the requirement that the sub-cyclic speed fl~c.uations must be measured on the fly, before full speed is achieved.

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This limitation is minimized to some extent by the acces-sory loading which requires a number of engine re~olutions before full speed is achieved. The use of the snap acceleration method for hot-testing engines outside of a vehicle where there is no accessory loading other than the engine flywheel is both impractical an2 potentially dangerous. The absence of load other than the flywheel results in: (1) insufficient sub-cyclic speed resolution, (~) rapid acceleration to maximum speed within a few revolutions which limits the time available to measure the sub-cyclic speed, and (3) the danger of exceeding maximum engine speed causing destruction of the engine Although these problems may be less apparent in diesel engines which have a heavy flywheel and, therefore, a large rotational inertia which results in ade~uate loading of the engine to provide sufficient resolution from which engine speed data may be obtained, and ~-ith the slow acceleration characteristics of diesel engines a sufficient number of engine revolutions of data are available befor~ the governor ~ontrolled maximum speed limit is achieved. On the other hand, spark ignition IC
engines generally have comparatively lightweight fl~wheels which (1) do not provide sufficient crankshaft loading to permit any reasonably accurate measure of acceleration,

(2) achieve full speed in only one or two revoluti~ns of the crankshaft which does not allow sufficient crankshalt data for accurate change in speed measure~lents, and (3) are not governcr controlled such that engine fly-away is ; a definite potential hazzard.
Although the hot-test engine may be loaded in a test stand with a selectable torque load, such as a dyna-mometer, thereby overcoming the deficiencies in load, data acquisition, and the potential fly-away problem, the load's rotational inertia contributes to the apparent engine torque while the engine is operating. This is due ...

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., to the "stored energy" in the load provided by its iner-tia which: (1) provides a drag to the engine crankshaft under change in engine speed, and ~2) contributes to maintaining shaft speed at the steady state value achieved prior to engine de-acceleration. This problem is even more manifest when the desired engine torque data is that occurring at sub-cyclic speeds, since the sub-cyclic speed fluctuations caused by the individual cylinder firing are significantly affected by the load torque contribution. This prevents the accurate measurement of torque and limits the relia~ility of the apparent torque measu~ements for use in diagnosing engine sub-cyclic performance.

, Disclosure of Invention One object of the present invention is to provide quantitative measurement of the sub-cyclic relative power balance between cylinders of an IC engine under extra-vehicular, hot-test conditio~s without loss of accurac~ due to load imposed d~ta distortion.
According to the present invention the individual cylinder contributions to the 1uctuations, or delta values, of the net sub-cyclic torque of the loaded engine, i provided as the difference between the delta sl-b-cyclic torque values of the engine an~ load over at least one engine cam cycle, are measured within the individual cylinder sub-cycle portions of the net delta torque data waveform; each cylinder contribution being compared with each other cylinder's ccntribution to prcvide individual cylinder inaices of the relative power balance of the engine. In further accord ;7i~h the presen, invention, the delta sub-cyclic torque values of the engine ana lcad are determined by sensing delta sub-cyclic speed values for each at selected c~anXsh~ft angles over one or more engine cycles, the sub-c-~clic s?eed values obtained are dilIerentiated ~ith respect to cran~shaft , ., ., .,.

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angle and multiplied by the total instantaneous speed value sensed at the particular crankshaft position to provide an indication o~ angular acceleration, the resultant acceleration indications for each are multiplied 5 by the associatea rotational inertia values of the engine and load to provide the delta sub-cyclic torque indica-tions for both engine and load over one engine cycle. In still further accord with the present invention the indi-vidual cylinder contribution to the net delta sub-cyclic 10 torque is measured by integrating the instantaneous net delta torque values provided by each cylinder over the crankshaft angle interval associated with each cylinder, each cylinder net delta torque integral summation being compared with each of the other cylinders to provide an 15 indication of relative power contribution. In still.fur-' ; ther accord with the present invention, each cylinder's contribution to the net delta torque is measured by the .' ' integration of the instantaneous values of net torque ` associated with each cylinder over a crankshaft sub angle 20 interval less than that associated with the full cylinder ,`. portion, the selected crankshaf't sub-angle interval bein~
~ e~ual for each cylinder, the ac:tual cran~shaft angle v valucs providing the sub-angle for each cylinder being selected in dependence on the particular model type IC
' 25 engine tested, ' The relative power contribution test of the present invention provides for the determination of overall ensine perIor.mance by analyzing ~he sub-cycli.c fluctua-tions in net engine torque at prescribed cran~shaft angle 30 intervals associated with each cylinder, thereby provid-ing an accurate measure of the engine relative po~er ~ alance at steady state engine speeds. These and other ',. objects, features and ad~antages OI the p~esent invention .~ will become more apparent in light of the de-tailed des-,' 35 cription of a best mode embodi-nent thereof, as illus~ated ~' in the accompanying drawing.

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- 5a -In accordance with a particular embodiment of the invention, there is provided an apparatus for measuring the relative power contribution between cylinders of an internal combustion engine running at a selected speed and connected through a crank-shaft coupling to the sha~t of an engine load to provide a common, loaded drive shaft. The apparatus includes engine speed sensing means which is responsive to rotation of an engine member mounted to and rotating with the engine crank-shaft. The engine speed sensing means provides an actual engine speed signal indicative of the instantaneous average engine speed and the instantaneous sub-cycle engine speed. The apparatus further includes a load speed sensing means which is responsive to rotation of a load member mounted to and rotating with the load shaft for providing an actual load speed signal indicative of the instantaneous average load speed and the instantaneous sub-cycle load speed. In accordance with the invention, the apparatus includes a signal processing means which is responsive to the actual engine speed signal ancl the actual load speed signal. The signal processing means has memory means for storing signals including signals indicative of the rotational inertia of the engine and load. The signal processing means provides, in response to the engine and load speed signals, signals indic-ative of the instantaneous, sub-cyclic angular acceleration of the engine and load over at at least one full engine cycle. It also provides, in response to the engine and load acceleration signals, signals indicative of the instantaneous, sub-cycle torque of the engine and the load as the product of the corresponding one of the acceleration signals multiplied by the associated one of the signals indicative of the rotational inertia of the engine and the load. The signal processing means is also adaptable to compare the sub-cyclic torque signals of the engine and load to provide a net sub-cyclic torque signal at a mag-nitude equal to the difference torque value therebetween. It is also adaptable to identify each sub-cyclic fluctuation in the net torque signal. Finally, the sensing means is adaptable to compare the magnitude of each of the sub-cyclic fluctuations to the ~' $``~
- 5b -magnitudes of all other of the fluctuations occuring in the common engine cycle to provide signal indications of the relative power contribution between cylinders.
From a different aspect, and in accordance with the invention, there is provided a method of measuring the relative contribution between cylinders of an internal combustion engine running at a selected speed and connected through a crank-shaft coupling to the shaft of an engine load to provide a common, loaded drive shaft. The method includes the step of sensing the instantaneous angular position of the drive shaft to provide position signals manifesting the instantaneous position of the engine crank-shaft at successive angle intervals within the engine cycle~ Each angle interval is less than that associated with a cylinder sub-cycle. A further step includes measuring the actual speed of the engine crank-shaft and the load shaft at each crank-shaft angle interval manifestation of the position signal to provide an indication of the sub-cyclic fluctuations in angular acceleration of each as they occur over one engine cycleO The method in accordance with the invention is character-ized by the steps of determining an engine torque signal andload torque signal over one engine cycle by multiplying the res~
pective values of angular acceleration by the rotational iner-tia of the engine and load. A net torque value for each crank-shaft angle manifestation is calculated as the difference values between the engine and load torque signals to provide an indic-ation of the sub-cyclic fluctuations in net torque over one engine cycle. Further, there is provided the step of comparing the magnitudes of said su~-cyclic fluctuations in net torque in a common engine cycle to provide signal indications of the relative power contribution between cylinders.

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Brief Description of Drawing Fig. 1 is a schematic block diagram illustration of the instrumentation in a typical engine hot-test instal-lation in which the present invention ma~ be used;
Fig. 2 is a system block diagram of a hot-test control system which may incor~c.ràte the present invention;
Pig. 3 is a system block diagram illus~ration of one subsystem as may be used in the control system embodiment of Fig. 2;
Fig. ~ is a system block diagram illustration of another subsystem as may be used in the control system em~odiment o~ Fig. 2;
Fig, 5 is a system block diagram illustration of still another subsystem as may be used in the control system embodiment of Fig. 2;
Fig. 6 is a simplified logic: flowchart diagram illustrating one functional aspect of the control system of ~ig. 2;
Fig. 7 A B is a simplified logic flowchart diagram illustrating one function of the present invention as performed by the control system of Fig. 2.
~ ig. 8 is an illustration of a set of waveforms charac'erizing one aspect of the dynamic performance of an engine under loaa which is used in ~he description of the present invention;
Fig. 9 is an iliustration of another set of waveforms characterizing another aspect of the dynam,ic performance of an engine under load which is sued in the description of the present invention; and Fia. 10 is a simplified logic flowchaxt diagram illus-trating the relative power contribution of the present invention ~s performed in the con,rol sys..em of Fig. 2.

.~99~- 5 Best ~iode for Carrying Out the Invention Referring to Fig~ 1, in a simplified illustration oE an engine hot-test installation in ~Jhich the presen~
invention may be used, a test control system 30 receives sensed engine data from the test engine 31 which is mounted in a test stand ~not shown) and loaded by connection of the engine crankshaft 3~
through a coupling assembly 3~ ts an ensine load, such as a b,ake mechanism or, as illustrated~ a dynamometer 1~ (dyne) load 36. The dyne is known type, such as th2 Go-Power Systems ~odel D357 water dynamometert equipped with an air starter 37. The air starter is used to crank the test engine (through the dyne) in the a~sence OL an engine mounted starter. A dyne flywheel 38, connected to the dyne shaft 40, includes a ring-gear (not shown) having a selected number o precision machined gear teeth equally spaced around the cir_u~-rerence of the ring-gear so that the tooth-to-L~oth intervals define substantially e~ual increments c dyne shaft angle. Dyne control circuitry 42 controls the dyne load torque tFt-Lb) to a set point torqu~ reference signal provided on lines a3 from the analog interconnect 44 of the control system 30, by controlling the amount of water in the dyne drum (not illustrated in Fig. 1)~
The dyne contlol circuitry also provides a sensed~
actual dyne torque signal on a line 45 to the analog interconnect of the control system.
The test engine is provided with the engine ` services 46 necessary for en~ine o?eration, such as fuel, oil, and water, etc. through service connections 48. The engine exha~st manifolds are connected throu~h exhaust line 50 to an exhcust evac~ating pum2 52 Following engine start-~p in response to a "start ~ en~ine'l d screte sign~l preserted on lines 53 to the .

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~3~6 , starter ~7 (or engine starter if available) from the control system digital înterconnect 5~, an engine throttle control 55 and associated throttle control actuator 56 control the engine speea ~RPrrl) to an engine RPM reference set point signal provided to the control on lines 57 from the analog interconnect~ Tn additiont the actuator receives a discrete signal fro~ the digital interconnect 54 on a line 58, which is used to provide snap acceleration of the engine as described hereinafter. In summary, the test engine under hot-test ~s operated under controlled load at selected en~ine speed profiles to per~it the dynamic analysis o the engine base-line parameters and the engine ~îagncstic routines described hereinafter.
The hot-test sequence examines engine base-line parameters related to speed, exhaust emission~, ignition cycle timing, and spark duration to determirle engine health, i.e., output power and combustion efficiency - The speed measurements include engine crankshaft speed ~RPM) and dyne shaft speed. The indication of engine crankshaft speed may be provided by any type of rotational speed sensing device, such as a shaft encoder5 or pre-ferably a magnetic pick-up sensor 60, such as Electro Corp. RGT model 3010-AN Magnetic Proximity Sensor, which senses the passage of the teeth cF the engine ring-gear mounted on the en~ine flywheel 62 and provides an engine series tooth pulse signal on the line 64 to the analog interconnect. The actual num~er o~ ring-gear teeth depends on the particular englne model with 128 teeth being average. The teeth are uniformly spaced around the circumference of the rinq gear, such that 128 teeth provide tooth-to-tooth spac- ~
ing corresponding to a crankshaft angle interval of ~ ~ .

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' 2.813 degrees. This is adequate for ~afk;ng subcyclic cylinder events within the ignition cycle, but due to the variation of total tooth count with different engine models it may be preferred to provide the crankshaft angle resolution required by the control system fro~
the load speed indication. The load speed ~ay also be sensed with a shaft encoder or by sensing the teeth of the dyne ring-~ear which has a tooth coun~ typically twice that of the engine ring-gear, or 255 teeth for the 128-tooth engine ring-gear. This is provide~
by a pro~imity sensor 66, similar to the sensor 60, which senses the passage of the dyne ring-gear teeth t~
provide a dyne series tooth pulse signal on line 68 to the analog interconnect The precision edging of the dyne teeth allows for exact resolution on the leadin~
and trailing edges of each of the tooth pulse si~nals which permits (as described in detail hereinafter) ed~e detection of each to provide an equivalent 51~ dyne ~- tooth intervals per crankshaft revolution.
Engine exhaust measurements include both exhaust gas analysis and exhaust back-pressure measure~ents~
The emissi~ns analysis measures the hydrocarbon ~C) and carbon monoxide tC0) constituents of the exhaust with an emissions analyzer 70, of a type known in the art such as the Beckman Inodel 86A infrared analyzer.
The analyzer is connected to the exhaust pipo 5~
through an emissions probe 72. The ~C an~ Co concen-tration is determined by the differential measure~ent of the absor~tion of infrared energy in the e~haust gas sample. Specifically, within the analyzer thO equal energy intrared beams are directed throhgh tw~ optical ., ,, .

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calls; a flow through exhaust gas sample cell and a sealed reference cell. The analyzer measures the difference between the amounts of infrared ener~y absor~ed in the two cells and provides, through lines 74 to the control system analog interconnect, HC and CO
concentrations as DC signals with full scale corre-sponding typically to: (1) a full-scale HC readinq o~
1000 PP~, and (2) a full-scale C0 of 10%. The analyzer operating modes are controlled by control signal discretes provided on lines 75 from the digital inter-connect. The exhaust back-pressure instru~,entation includes a back-pressure sensor 76, such as a Viatran model 21815 with a range of + 5 PSIG, and a back-pressure valve 73, such as a Paci~ic Valve Co. model 8-8552.
The pressure sensor is connected to the exhaust line 50 with a tap joint 80 and provides a signal indicative of exhaust back-pressure on line 82 to the analog in.er-connect. The back-pressure valve simulates the exhaust system load normally provided by the engine mu~fler and is typically a manually adjustable 2" gate valve with a range of 15 turns between full open and full clos~d~
The engine ignition timing information is derived from the crankshaft angle information provided by the dyne and engine ring-gear teeth and by sensing a crank-shaft index (CI), such as the timing marker on theengine damper 88. The CI is sensed with a magnetic pick-up sensor 90, such as the Electro Corp Model ~S~7 proximity switchl which preferably ls ~ounted through a hole provided on the damper housing and measures the passage of the timin9 marker notch on the damper. The sensor mounting hole is at a known crankshat angle value from the top dead center tTDcl position o~ the ~1 .3~

cylinder, and is determined from the engine specifica-tions. The notch trig~ers 3 signal pulse by passing near the CI sensor every cr~nksha~t revolution and the CI pulses are provided on lines 92 to the control system digital interconnect. In addition, the i~nition cycle inforrnation ir.cludes measurement of the ~1 cylinder sparkplug firing which in combination with the CI sensor indication provides a cranksha~t synchroniza-tion point corresponding to the TDC o~ the ~1 c~linder power stroke. The spark ~irin~ is sensed by a cl~mp-on Hall effect sensor 94 which provides 2 Yoltage sisnal pulse coincident with the sparkplug iring on a line ~6 to the digital interconnect.
The sparkplug signal duration measuremer,~s are provided by measuring the primary ~Lo Coil) and secon-dary (Hi Coil) voltage signals o~ the en~ine igni-ion coil 100. The Lo Coil voltage is sensed by a connec-tion 102 to the primary of the coil and the Hi Coi~
voltage is measured with a sensor 103, such as a Tektronix Model P601~ high-voltage probe wi~. a range of G to 50 KV. The signals are provided on lines 104, 106 to both interconnects of the control system.
In addition to sensing engine speedr exhaust, ignition timing and spark duration para~eters~ the ; 25 intake manifold vacuu~ pressure is also sensed. Two ~acuum measurements are made, a DC mani old vacuu~n which provides the average vacuum level t an~ an AC
manif~ld vacuum which provides instantaneous values of vacuu~. The AC measure~ents ar~ made ~y ~nsertin~ 2 ` 30 pressure sensor 108, such as a VIATRAN Model 21% with a ~, range of + 1 PSIG, in the ensine V2CUU~ line connected to the PCV valve. The DC manifold vac~um sensor llO

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may be a VIATRAN l~odel 218 ~ith a range of ~ 15 PSI~
inserted in the same vacuum line Each sensor provides a voltage signal indicative of the sensed pressure on lines 112, 114 to the control system Additional S engine sensors 115, sucn as pressure and temperature of the engine oil, fuel, water, etc. are provided to the control system through lines 116 The sensors provi~e the information on the necessary prerequisite engine ambient conditions which mus, be established prior to test, as discussed in detail hereinafter.
With the test engine connected to the load dyne 36 and instrumented as shown in ~ig~ Ir the ho~-test control system automatically programs the start-up (crankin~), ignition, and running of the engin2 at prescribed eng ne speed (RPM) and engine load condi-tions. Referring now to ~ig. 2, a hot-test control system 30 which may incorporate the present invention includes a central processing unit ~CPU) 130 which ~ preferably is a known, proprietary model general pur-pose computer, such a~s the Digital Equipment Corpora-; tion (DEC) Model PDP-llf34 minicomputer wbich ~ay be used with a software data system based on the DEC
RSXll-M multi-task real time software package. The size of the CPU depends on the data processing tas~s o~
the system, so that depending on the hot-test syste~
requirements, a smaller microcomputer, such 2S the DEC
LSI-ll, ~ay be used for th~ cPU. Si~;larly~ a number of smaller CPUs may be used, each dedicated to a par-ticular aspect or function of the system. ~he sele--tion of the particular type of CPU to be used is onewhich may be made by those skilled in the art, based on system throush-put requirements It should be understoodr however, that selectior of the particul~r type of CE:U is ~.~ 3~

de~endent on overall hot-test requirements alone, and forms no part of the present in~ention. If it is consid~red necessary, or prac~ical, any one of a number of known processing systems and soft~Jard packa~es may be used as may be obvious or readily apparent Lo those skilled in the art.
As-known, the CPU includes ~eneral purpose re~is-ters that perform a variety of functions and serve as accu~lulators, index registers, etc wi,h two dedicated lQ for use as a stack pointer (the locations, or address o~ the last entry in the stack or memory) a~d a pro~ram counter which is used for addressing purposes and which always contains the address of the next instruction to be executed by the CPU. The register operations are internal to the CPU and do not require bus cycles. The ; CPU also includes: an arithmetic logic unit (ALU), a control logic unit, a processor status register, and a read only memory (ROM) that holds the CPU source codet diagnostic routines for verifying CPU operàtion, and bootstrap loader programs ~or starting up the system~
The CPU is connected through input~output tI~O~ linos 132 to a processor data bus 134 ~hich includes both control lines and data/address lines and ~unctions as the interface between the CPU, the associated ~emory ~ 25 136 which is connected through I/O lines 138 to the ; data bus, and the peripheral devices includ7ns user equip~ent.
The memory 136 is typically nonvolatile, and may be either a core memory, or preferably a ~etallic oxide semiconductor (MOS) memory with battery ~ackup to main-tain MOS memory contents durin~ power interruption. The MOS memory may comprise one or more b2sic MOS memory ....

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units, such as the DC ~IOS memory unit ~ISll-JP each having 16 K ~ords of memory location, as determined by system requirements. The memory is partitioned into several areas by the system application software, as described hereina~ter, to provide both read only, and read/write capability.
The peripheral devices used with the CPU and memory, other than the user interface devlces, may include: (1) a disk memory loader 140, such as a DEC
Pac Disk Control unit with two dis~ ~rives, connected through I/O lines 142 to the bus, (2) a CR~/key~oard terminal 144, such as DEC ADDS model 9~0, connected through I/O lines 146 to the bus, and ~3) a printer 148l such as the DEC LA 35 printer, connected through I/0 lines ~50. The printer and disk loader are options, the disk memory loader being used to store bulk engine data or specific test routine instructions on floppy dis~s, which may then be fetched by the C~U. Al':e~na-tively, the specific test routines may be stored in the memory 136 such that the disk memory loader is used to store only bulk data.
The CRT/~eyboard unit provides man-machine interface with the control system which allows an operator to input information into, or retrieve informatlon from 2~ the system. These man-machine progra~s may lnclude general command functions used to start, stop, hold, or clear various test routinesr or to alter engine speed or dyne torque set point values for the engine throttle and dyne control circuitry In addltion, a specific "log-on" procedure allows the operator to alter the engine specification data stored in a data common portion of the memory 136.

The user interfaces include first and second digital interfaces 152, 154, and analoy interface 156, connected through I/0 lines 157-159 to the processor bus. Each digital interface receives the sensed engine data from the digital I~0 interconnect 54 on lines 160 ~he digital interface 159 provides the re~uired control system output discrete signals to the test engine instrumentation through lines 162 to the digital I~O
interconnect. ~he sensed engine data presented to the analog I/0 inte.connect 4~ is presented through lines 164 to the analo~ interface which provides the control system set point reference signals for the engine throttle and dyne control circuitry on lines 170 back to the analog interconnect.
In the operation of the CPU 130 and memory ~3 under the application software for the system, th.e memory is partitioned into a number oî different areas, each related to a different ~unctional aspect of the application so~tware. As used here, the term applic~-- 20 tion software refers to the general st~ucture and collectio~ af a coordinated set o~ software routines whose primary purpose is the management of svstem resources for control o~, and assistance to, the in-dependently executable test programs described indi-vidually hereinafter. The three major areas of th~
memory include~ a li~rary area for s~oring a collection of commonly used subroutines, ~2) 2 data common area ~hich functions as a scratch pad and which is accessible by other prosrams in mel~or~- ~hich require scratchpad storage, and (3) a general data acquisition ~L ~

program area which incluàes routires for: collecting raw data from .he user interfaces and storir.g the raw data in data common, deriving scaled5 floating point data from the raw data, and a sa~ety monitor su~routine which monitors some of the incoming data ~or abnormal engine conditions such as engine overspeed, low oil pressure, and excessive enqine block temperature~ In addition to the three main program areas, a further partition may be provided for a test sequencer program ~hich functions as a supervisory control of the engine hot-test sequence of operations.
The data common area is partitioned into su~-regions for: (1) storing the sensed raw data from the user inter~aces, (21 storing scaled data derived ~rom the stored sensed data by use of selected con~ersior~
coefficientsr (3) storing engine model specific~tions such as number of cylinders, firing order, CI sensor mounting hole angle, number of ring-~ear teeth, etc~, and (4) storing a description of the desired tes~ plan (a list of test numbers).
The areas in memory dedicated to the various test plans stored in data common (4) include a test module partition in which the engi:ne tests requested by the test sequencer progra~ are stored during execution of the test. The test~ stored represent separately built progra~ test routines executed durin~ hot-test, tha~
have a name format "TSTXXX" ~here XXX is a three-digit number. The test routines themselves are stored ei~her in a further partition of the memory 136 or, if optioned, stored on floppy disks and read into the test ~lodu~e partition from the disk driver.

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., Each CPU instruction involves one or more bus cycles in which the CPU fe~ches an instruct~on or data from the memory 136 at the location addressed by the program counter. The arithmetic operations perforl~ed by the ALU can be performed from: one general register to another which involves operations internal to the CPU and do not require bus cycles ~except for instruc-tion fetch), or from one me-nory location or peripher21 device to another, or between memory locations of a peripheral device register and a CPU general register;
all of which require some number of bus cycles.
In the control system embodiment o~ ~ig_ 2, a combination interrupt~noninterrupt mode of operation is selected, although if desired, total nonint~rrupt lS may be used with further dedicated program~ing. The digital interfaces 152, 154 esta~lish the processor interrupt mode of operation in which trle CPU reads particular sensed engine data from the analog interlace : in response to specific events occurring within each engine cycle. The interrupt mode includes several submodes in which the CPU is directed to read speci-fic input parameters, or combinations of parameters, depending upon the selected l:est. Each of the inter-rupts have an associated vec~ored address whlch directs the CPU to the particular input channels, or the locations in memory associated with the particular analog channel. These vectored interrupts are used .o cause the CPU to read at the particular selected interrupt time: (a) engine cam angle aloner ~) cam angle and one or more analog channels~ ~c) one or more analog channels without ca~ angle, and ~d) the spark dllration counter ~descrlbed hereinafter with respect ~3~

to ~ig. ~)~ In the absence of interrupts, I e., the noninterrupt mode of operation, the CPU reads the data provided at the analog interface continuously as a stand alone device. In this roninterrupt ~ode, the sa~ple sequence and sample time interval, typically one second, is ordered by the general data acq~isition routine which stores the raw data in the memory data common location.
The interface 152 ~rovides the interrupts recuired to synchronize the CPU data acquisition to specific, selected events within the en~ine cycle. Thîs is provided by synchronizing t~he CPU interrupts to crank-shaft angle position by: (1) sensing instantaneous crankshaft angle position from the dyne tooth signal in~ormation, an2 (2) detecting the crankshaft synchron-ization point (the TDC of the ~1 cylinder pow~r stroke~
by sensing the CI signal from the CI sensor (9Gt Fig 1) to~ether with the number one cylinder firing as provided by the spark sensor (9a, Fig 1), as described hereinafter. With the crankshaft inde~ marking the beginning of each engine cycle, the dyne tooth signal provides information on the instantaneous crankshaft angle position fro~n this crankshaft synchronization point, such that the entire ignition cycle may be mapped. As a result, cam cycle and subcyclic informa tion related to specific cylinder ~vents within the ignition cycle may be accurately tagged a~ corresponding to known crankshaft angle displacement frpm the syn-chronization point. The interface 152 then interrupts the processor at predetermined locations within the engine cycle, each identified by a particular crankshaf~
angle value stored in the memory 136 and associateG ~th .-...

-., ., , _ 19- i with a particular engine cycle event. In addition, the interface 15~ also provides CPU interrupt for~
the presence of number one cylinder spark ignition pulse, ~2) the rising edge of the Lo coil voltage r signal ~which indicates the availability of the ~
voltage to fire the sparkplug), (3~ the CI signal, and (4j a discrete SPARK DURATIO~ DATA ~EADY signal provided Xrom the digital interface 154 (described hereinafter with respect to ~ig. 4).
Referrir,g now to ~ig. 3, the interface 152 includes a general purpose, parallel in/out ~us interface 180, sucn as the DEC DRll-C, which interfaces the proce~sor bus 134 to the signal conditioning circuitry illustrated.
As known, the DRll-C includes a control status resister, and input and output buffer reqisters, and provides three functions including~ address selection logîc for detecting interface selection by the CPU, the register to be used, and whether an input or output trans~er is to be perfor~ed, and t2) control logic which permits 2Q the interface .o gain bus control (issue a bus requests) and per~orm program interrupts to specific vector addresses. The interrupts are serviced at two inputs of the bus interface; REQ A input 182, and REQ B input 184. Each input responds to a discrete presented to the input and, in the presence of such a discrete, qenerates the bus request and interrl~pt to the CPU over the bus I~O line 157. The interface also includes 16 pin user input and outpu~ connections 186, 188 for d2ta transfer betwee~ the signal condition~ng circuitry and 3C the processor.
The interface 152 receives: the engine CI, the Lo-Cclil signal, the number ~ne cylinder spark ignition . , . .

signal, and the dyne raw tooth signal on lines 160 frorn the disital interconnect 5~, and the SPARK DATA READY
signal on a line 190 fro~ the interface 154. Tne dyne tooth signal is presented to an edge detection circuitry 192 which detects the rising and fallin~ edges of each raw dyne tooth pulse and provides a signal pulse for each, resulting in a doubling o the ~re~uency, i.e , X
2 pulse count for each camshaft cycle ~engine cycle) Tne conditioned dyne tooth signal is presented on a~
output line 194 as a series pulse si~nal at a frequency ~wice that of the raw tooth signal. ~or a dyne tooth COUIIt of 25~ teeth the conditioned tooth signal provides 512 pulses per crankshaft revolution; eac~ pulse-to-pulse interval defines a crankshaft angle increment equal to 360/512, or 0.703 . Since eac~ ca~shaft cycle is equal to two crankshaft revolutions, or 720, the camshaft angle measure~ent revolution provided by the conditioned tooth signal is better than 0 . 1~ . .
The conditioned dyne tooth signal on the line I~l is presented to a ten bit counter 196 which counts the con-ditioned tooth signal pulses and provides a 10 bit binary count on lines 200 to the input 186 o~ the digital irter-face 180. The counter 196 provides a continuous count of the tooth pulses, continuou51y overflowing and star~-ing a new 10-bit count. The count ou~pu, fro~ t~e counter 196 is alsv presented to one input tA3 of a comparator 202 ~hich receives at a second input (B) a 10-bit signal from the user output 188 The comparator provides a signal discrete on an output line 204 in response to che condition P. = B.
.

-2l-The CI signal, the SPARK DATA READY signal, and the output of the comparator 202 on the line 204, are presented to the input of a multiplexer ~MPX) 206, the output of which is presented to a buffer register 208.
The ~o-coil voltage signal and the number one cyIinder spark signal are each presented to a second ~IPX 210, the output of which is connected to a second bu~fer register 212. The outputs of the registers 208, 212 are connected to the interrupt inputs 18~ 184 of the 1~ bus interface. The siynal select function provided by the MPX's 206r 210 is controlled by address si~nals from the CPU on the bus interrace output lines 214 r 216. The address signals select the inputs called for by the CPU dependin~ on the particula, test routine or engine condition to be monitored at the particular time. The inter~ace 180 also provides reset discretes ~or the registers 208, 212 on lines 218~ 220 follow--ng the receipt OL the buf~ered discrete at the interrupt inputs.
In opertion, the control system acquires camshaft synchronization by having the CPU provide a ~ELECT CI
address signal on lines 214 to the MPX 206. The next appearing CI signal is steered into the re~ister 20~
and read at the input 182~ The interface ~enerates a bus request and an interrupt bac~ throush the da'a ~us to the CPU, which when ready, responds to the Interrupt `~ by rea~ing the counter output on the ~ines 200 Th~
count value is stored in data common. The CPU processes a num~er of CI interrupts, each time reading the counter output. The ten bit counter provides alternating high and low counts on successive CI interru~ts, corres~onding .,.
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~3~6 to TDC of the power stroke and intake stroke Oc each en~ine cycle. Typically, the count samples at alternate interrupts are averaged to provide two average count signals corresponding to the two interrupts ln each cycle. The CPU next requests the number one cylinder spark discrete by outputting a READ NO. 1 SPARX address signal on the line 216 to the MPX 210~ In respor.se to each spark signal interrupt r the CPU reads the output o~ the counter 196~ Since the spark discrete signal appears only once in each engine cycle, as opposed to the twice appearing CI signal, the count corresponding to the spark discrete is compared to the two averaged count signals for the CI interrupt. The CI count closest to that of the spark count is selected as the CI corresponding to the number one cylinder po~er stroke. The CI sensor crankshaft angle displace~ent from true TDC is read from memory and the equivalent angle count is added to the selected CI count (CIp) to provide the crankshaft synch point coun~ which is stored in memory. The difference count between the spark count and synch point count represents the engine timing angle value, which is also stored in memory.
The subroutines for ca~shaft synchronization are described hereinafter with respect to Fig. 7 With the engine cam cycle defined ~y th~ stored count in memory the CPU may specify particular ca~shaft an~les at which it desires to read some o~ the engine sensed parameters. This is provided by reading the de~ired cam angle value from the memory i36 to the output 188 of the interface 180, i.e , the B lnput of the comparator 2C2. In response to the count on the lines 200 from the counter 195 being equal ~o the l.
_23- !
referenced count, the comparator provides a discrete to the MPX 206, ~hich is addressed to the comparator output by the appropriate "SELECT COMPARATOR" address on the lines 214. This interrupt is serviced in th.e same way providing a vectored address to the CPU and steering it to the particular one of the analog input channels.
Referring now to ~ig. 4, the digital inter~ace 154 also includes a digital bus interface 230 r such as ~
D.~ C. The interface 154 receives the sensed engine discrete si~nals including the Hi-coil and Lo-coil voltage signals on lines 160. The Lo-coil signal is presented to signal conditioning circuitry 232 which squares up the leading edge of the signal and provides the conditioned signal on a line 234 to the reset rRST) inp~t of a twelve bit counter 236 and to the enable (ENBL) input of a one-shot monostable 238 The Hi-coll signal is presented to a zero crossover circuit 24~
which when enabled provides t:he SPARK DATA READY signal on the line 190 in response t:o the presence of a zero a~plitude, i~e., crossover of the ~i-coil si~nal.
As described hereinafte~ with respest to the sparkplug load tests, each Hi-coil voltage signal which is representative of successive sparkplug voltage sig-nals includes an initial KV peak voltage ~ollowed bya plateau representative of the actual plug firing interval. The pe~k KV portion is followed by a ring- :
ing of the waveform which, in some lnstances, may be detected by the zero crossover circuit 2S a true cross-over, therefore, the crossover circuit is enabled on]yafter a selected time interval following the leading eàge of the Lo-coil signal. The enable is provided by . a decode circ~it 242 which senses tne output of the .

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counter 236 and in response to a count greater than that corresponding to a selected time interval, typi- ¦
cally 512 microseconds, provides an enable gate to the ; zero crossover circ~it. The SPAR~ D.~.T.~ READY discrete fro~ the 7ero crossover circuit is provided both to the input of the digital interface 152 and to a stop (5TP) input of the counter 236. A one ~egahertz signal ~rom a clock 244 is presented to the count input of the counter 236 and to the input o the monostable 238r the i 10 output of which is presented to the start ~S~RT) input of the counter.
The counter functions as an interval timer and provides an indication of the time interval bet~ieen the Lo-coil leadin~ edge and the Hi-coil zero crossover which corresponds to the ti~e duration of th~ spark~lug -voltage signal. In o~eration, the leadlng edge of the conditioned Lo-coil signal resets the counter and triggers the monostable which, following a prescribe~
delay (typically one clock period) starts the counter which then counts the one megahertz cloc~ pulses. In response to a lines 2~.6 count greater than 512, the decode 242 provides the enab:Le to the zero crossover circuit. At the Hi-coil crossover, the crossover circuit provides the SPARK DATA READ~ discrete on the `~ 25 line 190, which stops the counter and if selected Dy ,he CPU, interrupts the CPU via the dlgital interface 152. The interrupt causes the CPU to read the count at ~ in~ut 248 of the bus interface as an indication of the time duration of the sparkpl~g firing ~oltage Typi-- 30 cally, this s~arkplug duration count is read continu-ously by the CPU, which ~Jith the synchronization to the camshaft angle identifies each sparkplus signal ~ith its associated cylinder.
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: ::i The bus interface 230 also provides at a user output 250 the digital discrete signals corresponciing to the START ENGINE signal, and the discrete signals associated with the throttle 2ctuator ~56, Fig. 1~ and with control of the e~issions analyzer ~70 Fig. 1).
These discrete enable signals to the analyzer include flush, sa~pler drain, and sa~ple intake commands which cause the analyzer to function in a program, all of which is known in the art. All o~ the discretes are presented through output lines 252 to line drivers 254, the o~tput of which is presented through the lines 162 to the digital interconnect 54 Referrins now to fig. 5, the analog interface 166 includes an analog bus interface 260, such as the DEC
model ADAC600-11, having input/output sections 252, 264. The input section includes a series of data acquisition channels connected to a user input 266 r and an analog-to~digital tA/D) converter-for providinq the digital binary equivalent of each sensed ~nalo~ param-eter through the bus output 268 and lines 159a to the processor ~us. The output section includes a digital-to-analog (D/A) converter which receives the CPU ~utput signals to the engine on lines 159b and provides ,he ~; analog signal equivalent of each at a user output ~70 The CPU output signals include: the setpoint reference signals for the engine throttle control and the torque setpoint reference signal for the dyne c~ntrol all included within the lines 170 to the analog interconnect The sensed ensine signals presenteci to the analog 30 interface are signal conditioned prior to input to the -26-~ ~ 3~
bus interface. The Hi-coll voltage signal on line 164a is presented to a peak detector 27~ which sam-ples and holds the peak ~V value of the signal r and this sampled peak value is ~resented to the bus inter-face. The peak detector is resetable ~y an engineevent discrete, such as the trailing edge of low coil from the Lo-coil signal conditioner 273 ln the interface 156. The AC manifold signal is presented through a band pass filter 274 to the bus interface. The lîmits of the band pass filter are selected in dependence on the number of engine cylinders and the range o~ engine test speeds. The DC manifold vacuum signal, the dyne torque signal, the miscellaneous sensed signals including engine oil, water and fuel temperatures and pressures, and the emissions data (lines 164d ~ are couple~ to the bus interface through low pass filters 276 which reject any spurious noise interference on the signal lines. The exhaust back-pressure sense signal on a line 164j is presented to a band pass filter 278 - 20 prior to presentation to the bus inteL-face, with the limits selected based on the partic~lar engine and speed range.
The engine raw tooth signal and the dyne raw tooth signal on the lines 164h,i, are presented to associa-ted frequency to DC converters 280, 282. The output si~nals from the converters, which include DC and AC
components of the tooth signals, are pro~i~ed on lines -284, 286 to associated band-pass and low-pass filters.
The con~erted engine tooth signal is presented to lo~
pass filter 288 and band-pass filter 290, and the ~` converted dyne tooth siynal is presented to low-yass filter 292 and band-p~ss filter 294. The DC signals i . .
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., ' , . . .
, , -27~ '' from the low-pass filters 28%, 292 provlde the DC, or average enyine speed (~av) for the engine and load, and are presented directly to the bus inter~ace. The AC signal outputs from the band-pass filters, w~ose limits are selected based on the same considerations given for filters 274, ,78, are presented through AC amplifiers 296, 298 to the assoclated channels of the input interface 262 as the indications of the instantaneous, or AC speed ~ N) of engine and load.
As described hereinbefore, the general data acsui-sition routine collects the data from the analog bus interface 260 at a prescribed sample cycle, typical~y once per second. The raw data is store~ in one - section of the data common partition of the memory 136 and a data acquisition subroutine generates a se~ of scaled data from the raw data using linear conversion coefficients stored in a coefficient table in memory~
This second set of data is a properly s~aled set of floating point numbers and is used primarily by the dynamic data display prosrams (for display on the CRT, ~ig. 2) and for particular test subroutines which require slow spee~ data). In addition, the general data acquisition routine may also execute a sa~ety ~onitor subroutine which checks for ~vertemperature of the engine blGck and also low engine pressure limits.
Re~erring now to Fig~ 6, in a simplified flow chart illustration of the general data acquisition routine the CPU enters the flow chart follo~ing terminal interrupt 300 and executes the subroutine 302 which requires the samplin9 of all A/D data channels (i =
Erom the analog bus in~erEace ~260, Fig 5). The raw .

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data read from the A/D is stored in da.a co~on~ ~ollow-ing the raw data acquisition subroutine 309 calls for providing a sc21ed set of data from that sa~pled in 3G2. This begins with process 306 which re~uests the CPU to fetch the linear coefficients (~i,B) associated with the particular data channel (i = ~ from a coeffi-cient table in data co~mon. Process 308 request the linear conversion of the raw data to the scaled resul- J
after which instructions 310 call for storage of the scaled data in data co~.~on at an address C = i.
Decision 312 determines if the last conversion was also the last channel (i - ~) and if NO then instructions 314 requests an increment of the CPU address counter to the next address and the conversion.subroutine is ~ai~
repeated for each of the raw data values. ~ollowing the.completion of the linear conversion subroutines (YES to decision 312) the safety monitor subroutine 316 is executed.
- All of the engine test routines acquire initial value data relating to load s;peed and torsue as well as engine timing and crankshaft synchronization prior t~
takins the particular test routine engine data~ The analog values relating to load speed and torque are obtained under the general acquisition routine The engine timing and crankshaft synchronization is obtained under a separate subroutine. ReLerring now to Fig~
which is a simplified flowchart illustration o~ a preferred engine timing and synchroni~ation subroutine, the CPU enters the subroutine at 350 (~ig. 7A) and instructions 352 request the CPU to set the cr2nkshaf~
index (CI) interrupt counter at zero. Instruction3 354 , ~3~

request a max. CI interrupt count of ~ which is equal ' to t-~ice the number of desired ca~ cycles of data (~) since the crankshaft index sensor ~g0, Fig 1) provides two pulses in each cam cycle. Instructions 356 next request the read of average engine RP~ fro~ data common. Decision 358 deter~ines if the actual engine speed is above a mini~u~ speed required to insure valid data. If NO, instructions 360 display an error on the CRT, ~144, Fig. 2) followed by decision 362 which determines if an operator entered CLEAR has been made.
If there is a CLEAR of the test then the CPU exists the subroutine at 364. In the absence of an operator CLEAR
the CP~ waits in a loop for the minimum speed condition to be established. This is provided by decision 366 which determines if tne latest RPI~ is greater than ` ~inimum, and if NO then continues to display the error and look for a CLEAR in 360, 362. Once the ~inimum RPM
has been exceeded, instructions 368 request the CPU to select CI INTRPT which results in the address select to 20 the ~PX 206 of the digital interface 152 (Fig. 3) which monitors the CI pulse signal provided on a line 160a Decision 370 Monitors the CI interrupt and in the absence of an interrupt displays an error in lnstruc-tions 372, and looks for an operator CLEAR in instruc-25 tions 374. If a CLEAR is entered the CPU exits at 364, and if no CLEAR then decision 376 monitors the presence Ç of a CI interrupt. Following a CI interrupt instruction .
378 requests a read of the dyne tooth ~ignal count provided by the counter 196 (Fig. 3). The CPU
` 30 increments the interrupt counter in instructions 1 380 to mark the dyne tooth count and decision 382 ., ., .

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~., ~30_ determines if the present interrupt is odd or even. I~
odd the count is stored at location A and if even it is stGred at location B (instructions 384, 386~.
Decision 388 next determines if the interrupt is at the ~ax count N and if not then branches back to instruc-tions 368 to set up the next CI interrupt data acquisi-tion. If the maximum number of interrupts have been serviced instructions 390 and 392 request the avera~ing of all the stored count data in each of the locations A, ~ to provide an average A count and an avera~e fi count.
The CPU must identify which of the two interrupts occurring within the cam cycle is associated with the TDC of the ~1 cylinder power stroke. This is provided by an acquiring the ca~ angle data associated with ~1 cylinder spark ignition. In ~ig. 7B, instructions 39g set the ~1 spark interrupt to zero anG instructions 396 define the max spark interrupt count as ~l equal to the number of cam cycles of data to be acquired. The CPU then executes the subroutine to determine the cam angle position corresponding to the ~1 spark ignition~
This begins with instruc.ions 398 to select a NO 1 SPAR~ INTRPT. The decision 400 looks for the presence of a spark interrupt and if no interrupt appears within 25 a predetermined time interval the CPU again goes into a waiti~g loop which begins with the display o~ an error in 40~ and tne monitoring of an operator entered CLEAR
in decision 404. If an operator clears entered the CPU
exits the subroutine at 364. If no CLEAR, then the presence of a spark interrupt is continu~usly monitored in instructions 406.

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Following a spark interrupt, instructions ~08 read the dyne tooth signal count. Instructions 410 increment the spark interrupt counter by one and instructions 412 call for the stora~e of the spark count ~alue at location C. Decision 414 deterl~ines if this is the last spark interrupt to be serviced, and if not the CPU
branches back to instructions 398 to set up for the ne~t interrupt data read. ~ollowin~ the req~ested number of interrupts, instructions 416 request the averaging o all the count stored at location C to provide a C average count value.
With this information available, the CI interrupt associated with TDC of the power stroke can be deter-mined by comparing the two CI counts (odd/even) to the spark interrupt count. This is provided in instructions 418 et seq which first calls for calculating the difference (X) between the avera~e A and the average C
counts. Instructions 420 request the determination Oc the count difference (Y) between the B average ~nd the C average counts. Decision 422 colnpares the X and Y
counts to determine which is the largest I~ the X
count is larger, than instructions 424 store the Y
difference count as that representative o' the e~yine timing angle value. Similarly, instructions 426 call for storing the X count as the engine timing angle i~
it is the smaller of the two count differences Instructions ~28, a30 request the CPU store o the crankshaft index power ~CIp) as being equal to the count of the B average, or the A average, respectively In otner words, the particular one of the two counts received in the CI interrupt clos~st to the count .

correspondin~ to the sp~rk interrupt is then consldered - to be the CIp of ~1 cylinder. Instr~ctions 432 request the CP~ to read the angle (~) deEined by the engine manufacturer for the particular ensine which represents the angular displacement between the mcunting hole for the CI sensor in the damper housin~ ~nd the instantaneouS position of the damper notch at true TDC
of ~1 cylinder. Instructions 433 next request the equivaleAt count value associated with the displacement angle, and instructions 434 request the calculation o~
the cam cycle synchronization point, or true TDC o~ ~1 cylinder power stroke, as the sum of the cra.~kshaft index of the power stroke plus the count i~cremen.
associated with the displacement an~le. ~ollowing instructions ~34, the CPU exits the program at 364~
With the CPU synchronization to the ensine cran~-shaft, the sensed engine data at the analog 1ntera~e 158 (Fig. 2) may be sensed at any selected crankshaft ~ngle increment, down to the 0.7 degree resolutio~
provided by the conditioned dyne tooth signal to the interface 152. The particular selection of angle increment depends on the resolution accuracy re~uired o the measured data, or the frequency of data chanye with crankshaft angle. Typically, the selected anyIe 2~ increments may be three or four ti~es ~reater than the ~chievable an~le resolution, the limit2.ion due pri-marily to the processor overhead time t i.e., the i inability of the processor to gain access to and process the data within the equivalen. real time 30 Interval associated wit the 0.7 degree crenk anyle .

,, ,~ .
., ~1~3~ 6 interval. In general, each test routine includes its own, dedicated data acquisition subroutine for the particular paralneter of interest. The vario~s test~
read out the slower engine speed data from data com~on, i~
as provided by the general data acquisition routine This slower data includes, among others, the sensed miscellanëous sensors ~115, Fig. 1) data relatin~ to oil and water te~peratures, the choke position, and the average speed and load torque values, as may be necessary to deter~i~e iE the engine prequisite conditions have been established prior to tes,.
The description thus far has been of a hot-test installation and control system which is capable of providing a number of different automated tests for determining the performance of the test engine. The instrumentation descri~ed with respect to Fig_ 1 r a~d the control system of Figs. 2-5 to~ether ~ith the description of the application software includinq ~he general data acquisition, are illustrative o that required for a hot-test system capable of providil~g such a number of different performance tests The present invention ~ay be incorporated in such a syste~;
its use and implemen~ation in such a system, as described in detail hereinafter, represents the best mode for carryin~ out the invention. It should be unders,ood, however, that the invention ~ay be i~plemented lr. a simpler ~ystem which includes the engine load, but which includes only that sensing, signal condi~ioning, and signal processing apparatus re~uired for direct support o the invention.

-3~
In the present invention the relative power balance between the cylinders of an engine under load is obtained by comparing the s~b-cyclic fluctuations, or delta values in net engine torque produced by each cylinder over one engine cam cycle. The term net engine torque refers to the difference between the torque value measured at the engine fly~heel and the torque value measured at the load. For a constant full cycle, or average engine speed and aconstzn! load torque, the average net torque is zero. However, the fluctuations or delta values in engine speed within an engine cycle, i.e. sub-cyclic speeds, produced by individual cylinder firing within the cycle, xesults in sub-cyclic angular acceleration of the engine cra~kshaft and sub-cyclic fluctuations of the torque at the engine flywheel and the load. Since the fluctuations in engine torque are the direct result of the individual cylinder's performance, the relative magnitudes of the ~luctuations provide an indication of the relative power balance be-tween cylinders. The difficulty, however, is that the ~luctuations in torque c~t the engine and load are out of phase due to the spring modulus of the cou~ling (34, Fig. 1) and the rotational inertia of the load resulting in an error component in the apparent torque measurea at the engine fly~heel. Since the actual sub-cyclic fluctua~ions in engine torque are small to begin with in comparison to the average en~ine torque output, the error contribution o~ the load is conside-able and d~feats the ability to obtain a resolute power balance indication~ As such the present invention determines the sub-cyclic fluctuations in the net engine torque or, as referred to hereinafter, the net engine delta .... . .
i . torque ~hich is equal to the difference in the sub-,~" cyclic fluctuations in engine torque (engine delta ~,' 35 torque) znd load tor,que (load delta torque), all o~
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The present invention may be used to provide relative power balance measurements in any type of IC engine, both spark ignition and diesel, without limitation to the number or configuration of the cylinders of their firing order. Thè
invention may be used alone or may be used together with other test procedures in an overall hot-test system employLng test procedures disclosed and claimed in one or more of the following commonly owned, United States Patent ~os. 4,302~815 and

4,291,383 and Canadian Patent Application Serial ~os. 362,2~8, filed October 14, 1980 and 362,900, filed October 21, 1980.
~ eferring now to Fig. 8, the vectors 450 in illus-tration (a) depict the TDC of the cylinder power strokes for an 8-cylinder engine. The vectors are numbered 1 through 8 corresponding to the cylinder position in the firing order as measured from the camshaft synchronization point 452, obtained from the CPU to engine crank-shaft synchronization described hereinbefore with respect to Fig. 7. From the synchronization point (452) a full cam cycle of 720 may be mapped with the nominally anticipated TDC positions for each cylinder. The waveform 454 represents an assumed composite of the instant-aneous engine sub-cyclic speed (engine delta speed, ~Ne) values for the cam cycle of illustration (a), referenced to the average or full cycle engine speed (~eAV). The speed is for an assumed good engine and is obtained from the analog bus interface- the delta speed values from the AC amplifier 296 and the average values from the low-pass filter 288 (Fig. 5).

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In a similar manner, the waveform 4~0 of illustration (c) represents an assumed composite of instantaneous sub-cyclic load speed (load delta speed) values (~Nd) obtained over one cam c~-cle and fluctuating about the

5 average load speed value (NdAV).
As evident by comparison of the waveforms o illustrations (b) and (c) the delta load speed is out of phase with, and at a lower peak-to-peak amplitude than that of the engine delta speed. The phase shift and lower amplitude are due to the spring modulus of the clutch coupling ~34, ~ig. 1) which must be suffi-ciently flexi~le ~o prevent damage to the engine crankshaft and coupling during acceleration and decel-eration of the engine under load. ~nother cause of the lower load delta speed amplitude is the natural reso-nant frequency of the dynamometer which is much less than the sub-cyclic frequencies at the typical engine test speeds. As a result, the load delta speed wave-form tends toward saturation, i.e. sle~J rate limited.
As evident from the difference of the delta speed waveforms there exists a differenc~ in sub-cyclic angular acceleratic:n ~etween engine and load such that the sub-cyclic delta torque values at the engine and load must also be different. ~Yaveorms 470, 480 of illustrations (d) ~e) represent composites of the ir.stantaneous values of engine and load delta torque respectively, as may ~e obtained by differentiation of the engine and load delta speed waveforms of illus-trations (b) (c). In the present invention the engine and load delta speed values are obtained as a function of engine crankshaft angle (~e~ to provide identity of the individual sub~cyclic fluctuations as associated with a particular engine cylinder. As a result, different1ation of the engine and load delta speed values are first provided ~ith respect to crankshaft angle as opposed to real time. Using known ma~hematical ~3~

relationships the speed differentiated values d(ANe), d(~Nd) are converted to angular velocity by ud8 of the K~oWn derivative relationship d(f(~) ? = d (f(~)).d3 and then to ansular acceleration va~es, asd~escribedd~n detail in the analysis of Appendix A. To illustrate, the engine delta torque waveform 470 is obtained by first multipl~ring the point by point differentiated values of engine deltG speed ei~e~Ne , by the crankshaf~ angular velocity ddt which is equ~l to the su~mation of the average engine speed plus the delta speed value obtained at each cran~shaft interval, or d~e=NeAv+~Ne(9e). Each resu1-tant product is an indicda~ion of angular acceleration which is then multiplied by the rotational inertia value of the engine flywheel and a por,ion of the clutch coupling to provide representations o the instantaneous values o engine delta torque over the cam cycle.
In calculating the torque values the rotary inertia value is that of the engine fl~heel plus a portion of the coupling. The other cou~ling portion being allocat-ed to the load. These values are stored in data co~mon in memory. The load delta torque waveform 480 of ` illustration (e) i5 obtained in a similar manner, and point by point summation of the engine and load delta ~5 torque values at equal crankshaft angle values pro-duces a net engine delta torque wavefo m 490, as shown ; in iliustration (f). As shG~n the net d~lta torque sub-cyclic fluctuations have a lo~er pe~k-to-pea~
amplitude and are phase shifted from ~he engine del~a torque wa~eforr, 470. This amplitude chznge and phase shift results from removal of the load error contribu-tionto the engine delta torque. The load toraue contri-bution varies ~ith the engine ,est spee^` and with the type engine under test, such that the error contribu-tion is a variable which mus~ be facto-.^-d out to produce an accurate sub-cyclic torque .ndicatior~ i.e. the ne~
delta torque, or analysis. S ace ~he -r~ la?s the cam~

cycle based on the cranksha~t synchron'zation to predict the location of each cylinder power stroke, the phase shifting introduced by the dyne load delta torque makes correlation of the sub-cyclic fluctuations in engine torque to the particular cylinder producing the fluctua~
tion, or at the minimurr inaccurate. This, as shown in Fig. 8 is true even for a norm21 engine, with the result being the possible rejection of an engine based on an inaccurate power balance measurements due solely to the load distortion o~ the engine delta torque wave-form.
The load torque contribution to apparent engine torque is highly manifest during engine ~ailures. To illustrate, in Fig. 9 it is assumed that cylinder 5 has an ignition defeat, such as a shorted spark plug wire.
In illustration (a) vectors 450 again represent the TDC
position of the cylinder power strokes with cylinder 5 having a smaller amplitude as illustrative of that cylinder's loss of power. The loss of one cylinder results in. a lower sub-cyclic frequency component ap-proximately 1/~ in the engine/load system, and the lower natural frequency of the dyne causes amplifica-tion of the low frequency component, as illustrated by the resultant load delta speed waveform 500 in illus-~5 tration (b~. Resonance of the dyne causes ampli~ica-tion of the low-irequency speed component and a low-frequency modulatio~ of the engine delta speed wave-form 502 of illustration (c). The sub-cyclic ~luctua-tion of engine delta speed associated with cylinder 5 is illustrated by the speed delta pulse 504, ~lthouh the contribution of cylinder 5 to the delta speed waveform appears small, the distortion caused by .he low-frequency modulatîon prevents accurate discrimina-tion bet~een the bad cylinder contribution and the sub-cyclic fluctuations associated with the remaining good cylinders of the engine which are also dlstorted.

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Although, even with the excessive distortion of the : engine delta speed waveform, the engine failure could : be easily detected it would be impossible to isolate the sou.rce of the failure to the bad cylinder. In the net engine delta torque values for the cam cycle data, as illustrated by the wave~orm S06 in illustration (d), the lot~-frequency component is factored out resulting . in a substantially clean torque waveform from which the . faulted cylinder's contribution, as sho~.n by the sub-cyclic torque pulse 508 corresponding to the cylinder . 5 position, may be readily detected .
Referring now to Fia. 10, in a simplified flowchart illustration of the relative power contribution test of the present invention, as used in the control system of Fig. 2, the CPU enters the flowchart at interrupt 520 and executes subroutine 522 to determine `. if the prerequisite engine test conditions have been established. The prerequisite conditions go to verify-~: ing the load torque setting 2.nd to ensu ing that the engine has achieved thermostat control and selected ~;. .
average engine test speed. The engine test speed and .. load torque value (Ft-Lb) are selected to maximize the :................ work required o~ each cylinder, thereby creating higher rr peak-to-peak fluctuations in the sub-cyclic speed and enhancing the sub-cyclic net delta torque values ob-tained for analysis. In general this ma~imizin~ of .~ ~ cylin~el work occurs at lower engine speeds in co~bina-`~ tion with higher load torque values. O~ course, the values selected are engine dependent. ~ypical values ~ 30 for the assumed eight-cylinder engine are an engine speed of 1200 RP~ and load torque of 75 Ft-Lb. Prior ;~ to beginning the test the selected test s~eed and load . - tor~ue values are read out o~- the test ~12n in meInorv and provided through the analos interconnect LO the : 35 throttle and ~yne controls (55, 42~ Fig. 1) to esta-. blish the setpoint control li~.its for ea_h. Ther~ostat control is established by sensing the t.~er and oil .~`., '~:
,:;
,~.
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, ~ 1 ~::
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- ~o -temperatures from the miscellaneous sensors (115, Fig.
1). Failure to achieve prerequisite conditions results in instructions 524 displayina an error on the CRT (144, Fig. 2) and decision S26 determines whether or not an operator entered CLEAR has been made. If YES the CPU exits at 528, and if N0 then branches back to instructions 522. ~ollowing establishment of the prerequisite test conditions, instructions 530 request initial test condition para~eters from data common, which include average engine speed (NeAv) and average dyne speed (NdAV).
Following instructions 530, the CP~ perlorms the relative power contributIon test routine ~32. This ~egins with subroutine 534 which requests one or more (M) cam cycles of engine delta speed (QNe) values measured at selected, equal cran~shaft angle intervals.
The interrup~ mode established by the interface 152 is used to cause the CPU to read the instantaneous engine speed values at the analog bus interrace for 20 each selected crankshaft angle interrupt~ The cr~nX- -shaft angle interrupts having been angle intervals are equal and may be provided at any angle increment desir-ed down to the minimum crankshaft 2ngle resolution available, i.e. 0~7 for the selected dyne too~h sensor and signal conditioning described. The actual count '~ values associate~ with each cranksh2ft angle value with-in t~e cam axle are established fro~ the crankshaft synchronization subroutine of Fis. 7. For an M number of cam cycles of data, the cam cycle data sets are averaged to eliminate cycle-to-cycle variations and to provide a mean cam cycle data set. Subroutine 536 similarly collects and averages ~1 czm cycles of load delta speed ~Nd) data to pro~ide a mean cam cycle data set along the szme cam cycle angle increments used in the engine speed data acquisiticn.
Subroutines 53~, 540 determine t:~e net delta torque associzted ~-ith the englne a~d loGd. Subrou.ine :~ ~ 3~i$

538 requests the successive point differentiation of the mean delta speed data points for each as a function of crankshaft angle increment. Subroutine 5~0 first provides for conversion of the differentiated data into a real time indication of angular acceleration by multiplying each differentiated value by the instanta-neous speed value obtained at the same crankshaft ansle, as described in the derivation sho~n in Appendix A.
The resultant indications of real time -ngular acceler-ation for each cran~shaft angle increment is multipliedby the value of the rotational inertia value indications for the engine flywheel (Je) and dyne flywheel (Jd)(ob-tained from memory) to provide the delta torque v,~lues for the engine (Te~ and dyne (Td) at each crankshaft a~gle increment along the cam cycle. Subroutine 5~2 ne~t requests the net delta torque (~T) values as the equal crankshaft angle, point by point summation of the two delta torque values provided in subroutine 540.
The composite of the net delta torque data points are illustrated for a normal engine in Fig. 8, illustration ) and for a faulted engine :in Fig. 9 illustration (d).
Following ac~uisition of the net delta torque values for one cam cycle in subroutine 542, subroutine 544 next requests the integration of the sub-cyclic ~luctua-tion in net delta ~orque associated with each cylinder.The actual in~e~ration is an approxi~laticn o~ a line integral tak~n along each cylinder associated ~luctua-tion in the net delta torque data set. The integration limits mai~ vary anywhere bett~een the adjacent valleys marking each cylir,der contribution to the net torque fluctuation, as illustr~ted in Fig. 9 illustration (a) by the cross-hatch area 546 of the net delta torque pulse 548 associate~ with cylinder 2. The pulse !idth is de'ined by the crankshaft angle values associated 35 with the valleys 550, 552 OL the t~avelo~~ L desired the entire pulse may be intesrated, from valley to valley, t~hich results in the determina.~on of tne total area under the net tor~ue pulse. The s,me -~2-integration limits may be imposed for each of the other cylinder related torque pulses ~ith the resultant integral value for each cylinder being compared with each other cylinder to determine the relative power balance.
For the faulted engine condition of Fig. 9 the full area integration limits may be used to easily detect the faulted 5 cylinder. The full area integra-tion limits may not, however, be suitable for use ~ith a relative power balance test intended to detect more , minor engine malfunctions i.e. minor imbalances in the ', power contribution of each cylinder indicative of a potential future fault. This is evident from illustra-tion (f) of Fig. 8 where the net delta torque wave~orm 490 represents that obtained from an assumed normal engine. Greater discrimination in detecting the rela-tive power balance may be obtained from ~nowledge of the given test engine model characteristics, such that integration limits may be established to provide ~ 20 integration along that portion, less th~n the whole ; cylinder contribution envelope, which are kno~7n to pro-` vide a higher degree of fault: manifes-tation for the particular engine. As such, the particular line inte-~` gration limits may result in integral slices taken along a portion of each cylinder's contribution to the ne~ delta torque, as illustrated by the integral slice 560 for the net torque pulse 562 of the waveform ago (Fig. 8, illustration (f). The integral li~its for .~ the slice 5~0 may be selected to coincide with that ;: 30 sensitive portion of the net delta torque envelope as determined by the particular engine model character-istics. Whe~eas the full area integration limits illustrated in Fig. 9 are senerally applicable to any ensine cylinder configuration since ~ith full area 3~ intesration of each cylince- torque pulse the effec.s f OI valve overla? are in e~fect cancelled out, the ~'!, inte~ral slice limits must be selec~ed such that the valve o~erlap p-oblem is t~'-en into consider2tion.
:"~
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'' ~`:
' ' The net delta torque integrations of subroutine 544 are performed by the CPU ~Jith known graphical integra-tion methods. This may include rectangular or trapezoid-al methods of integration. The limits, whether full area or one or more integral slices, are provided either in the test plan routine if the relati~e power contribu-tion is to be performed on consecutive ones of the sa~e type of engine, or may be entered by operator entry through the keyboard (1~, Fig. 2). No matter what li~its are selected, the essential criteria is that each cylinder contribution is integrated over the same integral limits with respect to the cylinder's TDC such that the relative power balance comparison may be made.
Following suDroutine 5~4, subroutine 570 requests the determination of the relative power balance indica-tion for each c~linde~ Typically, this is provided as the ratio of each cylinder integral value ,o the average integral value measured ~or all cylinders. The relative power balance indices for each cylinder a~e then stored, or displayed, or both, in instructions 572, after which the CPU e~lts the program cat 52~. The typical format for displaying the relative power contri-bution, or power balance indications, is illustrated in Table 1 for an engine having P number of cylinders.
~ABLE I
CYL ~ 1 2 . . . . . . .~
INT VAL Kl K2 . . . . Kp RPC 1 2 . . . . p a ~ a Each integral summaticn of ,he par,icular cylinder's contribution to the fluctu2tion in sub-cyclic net torque is lis~ed as intesr21 su~"at;ons '~1 through Kp, and the rela ive po~?er contribution of each cylin-der is lis,ed 2S the ratio of each inàividual cylind2r ; 35 integral su~ divided by the aver2ge inLecral value (K ) for the P cylinder int2srals. Typically, the pO?er contribu'ion va'ue o~~ain2d -o- ea_h c~linde- ~,ay be read as a percentage value with the tolerance esta-blished for the acceptable performance being defined as a percentage of power and balance.
Since measurement of power contri~ution is on a relative basis the co~parisons of each cylinder's contribution need not be based on absolute values. The net delta torque value, although it may be obtained as an absolute value using actual engine and load rotation-al inertia values, may similarly be provided as a ratio of net delta tor~ue divided by the engine rotational inertia. This ratio is equal to the time differentiated indication of engine delta speed plus the time differen tiated indication of load delta speed multiplied by a ratiometric factor equal to the ratio of the load inertia divided by the engine inertia. The efect is that al~hough the quantity is not pure net delta torque, the proportionate magnitudes of the engine delta torque and load deita torque values are properly scaled to re-flect the contribution of each to the net delta torque value. In other words~ although a rigorous, and per-haps preferred indication would be the absolute net delta torque, an indication of net delta torque which reflects the contribution o the engine and load may also be used.
The relati~e power contribution of the present `~ inventio~ provides a quantitative meGsurement standard by which engin2 performance may be measured, and wi,h which a non-subject;ve, quality pass/fail criteria ma~
` be established for testing engines under hot-test.
The relative power contribution is performed with the engine under load and running at essentially constant speed, thereby eliminating the limitations of the snap acceleration po~er contribution method used in vehicle mounted engines. The effects oî the ensine load ~hich result in data distortion are eliminated by use o- the net delta torque vslue. The sub-cycllc luctuations "
"
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-~5-produced by each cylinder are accurately ~easure~ by e~act identificaticn or each cylinder contribution along the cam cycie, provided through synchronization of t`ne power contribution data acquisiticn to the engine crankshaft.
The present invention may be used in determining relative power balance of any type o~ IC engines. The engine load may be any type suitable for providin~ a selectable torque load on the engine crankshaft.
Similarly, although the invention has been shown zna described with respect to a best mode embodiment there-of, it should be understood ~y those s~illed in the art that the foregoing and various other changes, omissions and additions in the form and detail thereof ~ 15 may be made therein without depaxting from the sp~rit ; and scope o~ this invention.

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~L ~b 3~ 6 APPENDIX A
PO~^~7~P~ CONTRIBUTION ANALYSIS

Let: Te = Engine Output Torque.
Td = Applied Average Load Torque.
0e = Shaft Position of Engine Crank Shaft 0d = Shaft Position of the Load.
Je = Rotary Inertia of the Engine Flywheel and a Portion of the Coupling Mechanism.
Jd = Rotary Inertia o the Load, the Starter Flywheel, and a Portion of the Coupling.
K = The Spring Modulus of the Clutch Coupling.
Assuming friction is negligible, then:
Te ~ Je d 3e + ~ ~0d-~e) = 0 (1) dt and Td + Jd d 9d _ X ~d-~e) = 0 (2) dt2 Summing equations (1) and (2):
Te + Td = -Je d ~e -Jd d ~e t3) dt2 dt2 Assuming a stead~-state loaded condition:
Te = T(nominal) + ~T (4) Td - -T(nominal) ~herefore, -~T = Je d20e ~Jd d29d (6) dt2 dtZ
This r~presents the fundamental dynamic equation usea in the test. Since the inertias for a given system are constants, delta torque output can be calculated by sensing the speeds of the masses and computing a time derivative as described below.
Engine speed (Ne = dt ) is input to the computer as two signals, Ne(avg~ and ~Ne where Ne(avg) represents the steady sta-e speed and ~Ne is a function of engine sha,t angle (~e). Using ~he basic derivative relationship, - [f(u)~ = d-u Cf(U)~ dx ... .

:

: . -.., ~3~

then:
d2~e d d~e = CNe~avg)+~Ne(ee)~
dt2 dt dL dt o~ :
d2ee = _ CaNe(9e)] caNe(avg)~aNe(6e)~ (9) dt2 d9e In a similar manner, the load acceleration is:
d 9d = d C~Nd(~e)]~[Nd(avg)+~Nd(ee)] (10) dt2 dad , ., ,., ,~ .
,'", .., ., .

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. Apparatus for measuring the relative power contri-bution between cylinders of an internal combustion (IC) engine running at a selected speed and connected through a crankshaft coupling to the shaft of an engine load to provide a common, loaded drive shaft, comprising:
engine speed sensing means, responsive to rotation of an engine member mounted to and rotating with the engine crankshaft, for providing an actual engine speed signal indicative of the instantaneous average engine speed and the instantaneous sub-cyclic engine speed;
load speed sensing means, responsive to rotation of a load member mounted to and rotating with the load shaft for providing an actual load speed signal indica-tive of the instantaneous average load speed and the instantaneous sub-cyclic load speed;
as characterized by:
signal processing means, responsive to said actual engine speed signal and said actual load speed signal, and having memory means for storing signals including signals indicative of the rotational inertia of the engine and load, for providing, in response to said engine and said load speed signals, signals indica-tive of the instantaneous, sub-cyclic angular acceleration of the engine and load over at least one full engine cycle, for providing, in response to said engine and load acceleration signals, signals indica-tive of the instantaneous, sub-cyclic torque of the engine and the load as the product of the corresponding one of said acceleration signals multiplied by the associated one of said signals indicative of the rotational inertia of the engine and the load, for comparing said sub-cyclic torque signals of the engine and load to provide a net sub-cyclic torque signal at a magnitude equal to the difference torque value there-between, and for identifying each sub-cyclic fluctuation in said net torque signal, and for comparing the magnitude of each of said sub-cyclic fluctuations to the magnitudes of all other of said fluctuations occurring in a common engine cycle to provide signal indi-cations of the relative power contribution between cylinders.

2. The apparatus of claim 1, further comprising:
position sensing means, adapted to be disposed along the common drive shaft for providing signals indi-cative of the instantaneous annular position of the engine crankshaft at crankshaft angle intervals less than that associated with a cylinder sub-cycle; and crankshaft index sensor means, disposed on the engine, for providing in each engine cycle a signal indicative of the occurrence of a selected engine cycle event; wherein said signal processing means is responsive to said position signal and said crankshaft signal, for providing signals indicative of each cylinder power stroke in each engine cycle, for sensing said actual engine speed signal and said actual load speed signal in response to each crankshaft angle interval manifestation provided by said position signal, to provide for each crankshaft angle interval a value of said net torque signal associated therewith, and for comparing said cylinder power stroke signals with said net torque values associated with each crankshaft angle interval to provide identification of each sub-cyclic fluctuation in said net torque with an associated one of said cylinders, whereby said signal indica-tions of relative power contribution is provided for each identified cylinder.

3. The apparatus of claim 1, wherein said processing means provides said signal indications of relative power contribution as the ratio of the magnitude of each of said sub-cyclic fluctuations in said net torque signal to the average of the magnitude of all other of said fluctuations in a common engine cycle.

4. The method of measuring the relative contribution between cylinders of an internal combustion engine running at a selected speed and connected through a crankshaft coupling to the shaft of an engine load to provide a common, loaded drive shaft, comprising:
sensing the instantaneous angular position of the drive shaft to provide position signals manifesting the instantaneous position of the engine crankshaft at successive angle intervals within the engine cycle, each angle interval being less than that assocatied with a cylinder sub-cycle;
measuring the actual speed of the engine crankshaft and the load shaft at each crankshaft angle interval manifestation of said position signal to provide an indication of the sub-cyclic fluctuations in angular acceleration of each as they occur over one engine cycle;

as characterized by:
determining an engine torque signal and load torque signal over one engine cycle by multiplying the respective values of angular acceleration by the rota-tional inertia of the engine and load;
calculating a net torque value for each crankshaft angle manifestation as the difference values between said engine and load torque signals, to provide an indication of the sub-cyclic fluctuations in net torque over one engine cycle, and comparing the magnitudes of said sub-cyclic fluctuations in net torque in a common engine cycle to provide signal indications of the relative power con-tribution between cylinders.

5. The method of claim 4, further comprising the steps of:
sensing a crankshaft index to provide a syncfiro-nization signal definitive of the occurrence,in each engine cycle of a known engine cycle event; and determining from said synchronization signal and said position signals the crankshaft angle intervals associated with each cylinder;
as characterized by the further step of:
relating said sub-cylic fluctuations to said angle intervals associated with the cylinders, to identify each of said fluctuations with an associated one of the cylinders, whereby said indications of relative power contributions are provided for each identified cylinder.